High-frequency generator



Sept 15, 1953 w, R. HEWLETT mm HIGH-FREQUENCY GENERATOR Filed March 6, 1950 2 Sheets-Sheet. l

INVENTORS W/l/iam R. Hew/e H W howaro M Ze/d/er HTTURNE Y5 p 1953 w. R. HEWLETT ET AL 2,652,511

' HIGH-FREQUENCY GENERATOR Filed March 6, 1950 2 Sheets-Sheet 2 Patented Sept. 15, 1953 UNITED STATES TENT OFFICE HIGH-FREQUENCY GENERATOR fornia Application March 6, 1950, Serial No. 147,870

(Cl. 3l51) 6 Claims. 1

This invention relates generally to high frequency electrical generators of the type commonly known as reflex klystron oscillators.

Reflex klystron oscillators have commonly uti lized resonators of the coaxial type, having a cylindrical outer conductor. For the higher frequencies of operation, such as from 4000 to 8000 megaeycles, such a resonator must have a relatively small internal diameter, and this imposes a limitation upon the oscillator design, particularly in that no adequate space is afforded for accommodating supplemental electrical devices, such as means to suppress an undesired cavity mode of oscillation. In addition prior reflex klystron oscillators have not been provided with adequate means for suppressing a cavity mode which tends to interfere with the desired mode of operation, particularly where the oscillator must be capable of adjustment to operate at a selected frequency over a relatively wide frequency range. Assuming for example that an oscillator is designed to operate upon the A; wavelength cavity mode of the cavity resonator, it is recognized that the 4 wavelength cavity mode may cause interference, and that it is desirable to suppress the 4 mode where the frequency of operation is over a range of say from 4000 to 8000 megacycles.

It is an object of the present invention to provide a reflex klystron oscillator which makes use of a cavity resonator of special construction which affords ample space for the mounting of special elements or devices.

Another object of the invention is to provide an Oscillator of the above type having novel means for suppressing an undesired cavity mode of oscillation and which will be adjustable to enable operation over a wide frequency range.

Another object of the invention is to provide an oscillator of the above type which is well adapted for use with very high frequency signalling equipment, and which will afford stable operation with a minimum amount of frequency interference for a wide range of frequency adjustment.

Additional objects of the invention will appear from the following description in which the preferred embodiment of the invention has been set forth in detail in conjunction with the accompanying drawing.

Referring to the drawing Figure 1 is a side elevational view in section illustrating a high frequency electrical generator incorporating the present invention.

Figure 2 is a cross-sectional view taken along the line 2-2 of Figure 1.

Figure 3 is a cross-sectional view taken along the line 33 of Figure 1.

Figure 4 is an enlarged cross-sectional detail illustrating the mode suppressing means emplcyed, and the elements used for its automatic adjustment.

Figure 5 is a cross-sectional detail taken along the line 55 of Figure 4.

Figure 6 is a schematic View illustrating the circuit connections for the various elements of the reflex klystron tube.

Figure '7 illustrates curves to show the movements of the suppressor probe.

In general the present invention comprises a cavity resonator having means for receiving a vacuum tube of the reflex klystron type, such as the tube known by manufacturers specifications as No. 5721 (Raytheon) A special form of cavity resonator is employed, and for a portion of the permissible frequency range of operation, special means is employed to suppress the A, wavelength cavity mode.

Referring first to Figures 1 to 5 of the drawing, the cavity resonator employed consists of the conducting plates or slab-like walls I0, together with a central conductor II. The two plates I0 are parallel, and also parallel to and equally spaced from the 'axis of the center conductor H.

The margins of the walls I0 extend for a substantial distance beyond the sides of the center conductor III, as viewed in Figure 1. Thus one obtains the effect of a slotted outer conductor, with the electromagnetic field being relatively intense in the region surrounding the center conductor, and decreasing rapidly toward the side edges of the walls I0. In actual practice it is desirable that the lateral extent of each wall Ill be more than twice the spacing between the walls.

At the forward end of the cavity the walls I0 are attached to the metal end wall [2, which forms a mounting for the reflex klystron tube I3. Also it is desirable to provide a rear metal wall It, which forms a mounting for the adjacent end of the center conductor II.

The two side edges of the cavity may be open, but are preferably closed by the walls I6.

An adjustable plunger I1 is fitted within the cavity to enable adjustment of the frequency of operation. This plunger consists of a metal body 58, which has a center opening I9 to accommodate the center conductor II. The forward end portion of the plunger carries spring finger contacts 20, which have good electrical contact with the inner surfaces of the walls I0, and like contacts 2| which engage the center conductor I I. Rods 22 extend through the end wall I4 and are attached to the plunger to enable adjustment to a desired position.

The klystron tube l3 may be of conventional construction and includes a heated cathode, a control grid, a repeller or reflecting electrode, and two resonator grids which are interposed between the cathode and the repeller. One grid is connected to the terminal ring 23, and the other to a cylindrical termina1 24. The repeller is connected to the end terminal 26, which can connect to a conductor extending through the bore 2! formed in the center conductor I I. The base 28 of the tube carries the usual terminals for making connection to the cathode and to the cathode heater.

When the tube I 3 is in normal position as illustrated in Figures 1 and 2, the terminal ring 23 is engaged by the coiled wire spring 29, which is retained within an annular recess 3! formed in the wall l2. The end portion 32 of central conductor II is slotted as shown and the cylindrical terminal 24 is received within this slotted end portion, thereby forming an electrical connection between cylindrical terminal 24 and the end portion 32.

Assuming a range of movement of the plunger I! to secure a wide frequency adjustment of say from 4000 to 8000 megacycles, for a substantial portion of this frequency range, as for example 4000 to 5500 megacycles, there is a tendency toward cavity mode interference. We have found it desirable to operate upon the A; wavelength cavity mode, and for that portion of the frequency range mentioned, there is serious interference by the wavelength cavity mode. We provide means on the plunger ll to suppress the wavelength cavity mode, and a particular feature of this means is that it is automatically retracted and made ineffectual for a portion of the frequency range for which it is not required. and for which it might interfere with operation upon the desired mode.

The mode suppressing means which we employ consists of a probe 36 which is preferably in the form of a pin made of lossy or dissipational material. It may for example be made of dielectric material such as a molded phenolic condensate product, coated with carbon to provide substantial ohmic resistance. One end of the pin 36 terminates a short distance from r the central conductor H, and the other end is secured to a shank 31, which is secured to member 38. Member 33 is slidably fitted within the slotted guide sleeve 39 which is carried by the body of the plunger [7. Member 38 is urged by compression spring 4| to the position shown in Figure 1, in which it engages the limiting shoulder 42. When member 33 is moved toward the body of the plunger H, the pin 33 may assume a position in which it is accommodated in a recess 43 which is formed in the adjacent face of the plunger body l8.

Mounted upon the forward wall l2 there is a stud 44 which is bored to receive the rod 46. One end of this rod carries the member 4?, which is adapted to engage the member 38. The other end of the rod is urged by the compression spring 48 toward the position illustrated in Figure 1.

Spring 48 is stronger than spring 4! and, in its extended position, exerts more force than does spring 4| in its fully compressed position. Hence, when plunger I1 is moved to the left from the position shown in Figure 1, member 38 is brought into engagement with member 4! with the result that no movement of member 41 or rod 46 occurs, and no compression of spring 48 occurs, until movement of plunger I! has caused the probe to become fully retracted into recess 43 and the spring 41 to become fully compressed. At this point of movement of plunger 1?, then, spring 48 is fully extended, spring 4! is fully compressed, and probe 36 is fully retracted into recess 43. As movement to the left of plunger 11 continues beyond this point, movement of member 47 and rod 46 and compression of spring 48 begins, and for movement of plunger ll from this point to its limit of movement to the left toward metal end wall I2, the probe 36 is thus in its fully retracted position within recess 43.

The circuit diagram of Figure 6 illustrates electrical connections to elements of the reflux klystron tube, and to external sources of current. The various parts have been simplified and illustrated schematically to facilitate explanation of the complete circuit.

The elements of the klystron tube include the cathode 5| which is associated with the heater 52, the control grid 53, the resonator grids 54 and 55, and the repeller 56. A source of current 51 has its positive side connected to the cathode 5|, and is connected to repeller 56 through the potentiometer 58. A battery or other voltage source 59 has its positive side connected to the external grounded conductor of the resonator, and its negative side connected to the cathode. The grids 54 and 55 are respectively connected to the external and central conductors of the resonator. The contro1 grid 53 is connected to the cathode or negative side of voltage source 59 through resistor 60, and is also connected to the positive side of the source of bearing voltage 6|.

Operation of the circuit shown in Figure 6 is known to those skilled in the art and need not be described. It will be evident that the voltages applied to the control grid 53 and the refiector 55 should be adjusted for stable oscillation on the wavelength cavity mode, for the various positions of the plunger. The output wavelength varies with the effective length of the cavity, but this is an approximate rather than an exact proportionality due to such factors as corner effects, presence of the klystron tube in the cavity, etc.

As shown particularly in Figure 2, tubular fittings 63 and 64 are carried by the walls 10, and afford passages 66 and 61 to facilitate introduction of coupling means for supplying energy to an external load, or for introduction of devices such as voltage attenuators, filter sections, or the like.

The curve of Figure 7 will afford a better understanding of the motion of the suppressor probe relative to the positioning of the plunger. In this figure the position of the cavity plunger for full frequency range adjustment has been plotted on the horizontal axis, and the position of the suppressor probe relative to the plunger plotted on the vertical axis. Curve l represents positioning of the probe relative to the cavity plunger. The portion la of this curve is parallel to the base line, and represents fixed positioning of the probe with respect to the cavity plunger for adjustments of the cavity plunger over the distance a. The curb portion lb represents the retraction of the probe for movement of the cavity plunger over the distance I). For adjustments of the plunger over the distance 0, the probe is fully retracted Within the recess 43.

ey d which point ppression is not required.

Curve ,2 represents the ideal relationship whi h is approximated by ,curye i. Curve illustrates a gradual shifting of the position of the probe relative to the face of the plunger, over the distance c that portion .of by the ideal curve 2, that is, distance a plus any u h r ista ce unt l po nt e i ached, bey which point suppression is not required. For such plunger movements, the probe remains at a distance from the face of the plunger equal to one-quarter of the undesired cavity mode wavelength, in contrast with the approximation of curve i where this wavelength proportionality is not maintained at all points. While theoretically desirable, it has been found that such gradual retraction or shortening of the distance between the probe and the face of the plunger, as the plunger is advanced for higher frequencies of operation, is not necessary for good stable operation, and that an acceptable operation with the desired suppression of the ,4; wavelength cavity mode is obtained by the approximation of curve I.

As an example of actual practice, we have obtained good results with a cavity having a Spacing of 1.7? centimeters between the walls I0, and with each Wall having an over-all width (between walls 16) of 7.6 centimeters.

The distance of movement of the cavity plunger ill for a frequency variation of from 4000 to 8000 megacycles was 3.3 centimeters. In its most forward operating position the effective front of the cavity plunger was 1.8 centimeters from the opposed face of the wall i2. The probe pin 30 was spaced 3 millimeters from the side of the center conductor 5 l, and was disposed 9 millimeters from the effective front face of the cavity plunger for the position illustrated in Figure l. lhe plunger had a movement of 1.1 centimeters for distance a, 1.0 centimeter for distance *0, during which the probe retracted, and 1.2 centimeters for distance 0 with full retraction of the probe. Approximately, the frequency range for adjustment over distance a. was 4000 to 5000 megacycles, for adjustment over distance b, 5000 to 6000 megacycles, and for adjustment over distance c, 6000 to 8000 megacycles.

It will be evident from the foregoing that we have provided a high frequency generator capable of stable operation over a wide range of frequencies, and without cavity mode interference. The construction and arrangement of the parts is greatly facilitated because of use of a cavity resonator of the slab type as described, particularly in that this affords ample space on one side of the center conductor for accommodating the probe 35, and the parts associated with the same.

We claim:

1. In a high frequency electrical generator, a reflex lrlystron vacuum tube having cathode, control and resonator grids and a repeller, a cavity resonator coupled to the tube for generation of high frequency, and including an outer conductor forming sides of a cavity, one end of distance 21 occupied the @cavity resonator being formed by a conduczt ye :plungerradjustable longitudinally of the same --.ca.vi y made, ai mean compri in a pr b I med ref material capable 10f dis ipat g f .ecluency ener y, tha e d fa of t e plu f accd toward the interior of the :cavity being formed rte provide :a :recess senving to accommoidate gsa-igl means mounting the probe for 7 oyernent from p ne position in advance of the ng and the recess for suppressing an undeto e. retracted position within said recess, and means tor effecting movement of said osi-tiens of the same responents of the plunger, said last mea s in lre a member dap d o engage .wd apply fierce to the probe to urge the same teward 1. d etracted position responsive to :adcausing tho rent of the plunger toward the interier cf .cayity tp increase the frequency cerat on. 2. in a high frequency electrical generator, a

reflex :k-lrstron vacuum tube having cathode,

control and resonator grids and a repeller, a cavity resonator including an outer conductor electrically connected to one resonator grid of the tube and a center conductor connected to the other resonator grid of the tube, one end of said cavity resonator being formed by a conductive plunger adjustable longitudinally of the same to change the frequency of operation, and means carried by said plunger to suppress an undesired cavity mode, said means comprising a probe formed of material capable of dissipating high frequency energy, a recess in the plunger serving to accommodate said probe, means mounting the probe on the plunger for movement from one position in advance of the plunger for suppressing an undesired mode, to a retracted position within said recess, and means for effecting automatic movement of said probe between said positions of the same responsive to adjustments of the plunger, said last means comprising a spring urged member disposed to engage said probe as the plunger is advanced into the cavity to thereby effect retraction of said probe into said recess.

3. A high frequency electrical generator comprising a reflex klystron Vacuum tube having cathode, control and resonator grids and a repeller, a cavity resonator having an outer conductor connected to one resonator grid of the tube and a center conductor connected to the other resonator grid of the tube, said outer conductor including two slab-like substantially parallel conducting walls disposed upon opposite sides of the center conductor, a rectangular plunger fitted between said walls and having a central aperture to receive said center conductor, and cavity mode suppressing means disposed in that space formed between said walls on one side of the center conductor, said means including a probe and a mounting for the same carried by said plunger.

4. A high frequency electrical generator as in claim 3 in which said mounting for the probe permits movement of said probe from one limiting position in advance of the plunger to a second limiting position within a recess formed in the plunger face, together with spring means for urging said probe to said first named limiting position, and means for causing automatic retraction of said probe to said second named position as the plunger is advanced into the cavity, said last means including a member adapted to engage and apply force to the probe to urge the same toward said retracted position responsive to movement of the plunger in a direction to advance the same into the cavity.

5. A high frequency electrical generator comprising a reflex klystron vacuum tube having cathode, control and resonator grids and a repeller, a cavity resonator having an outer conductor connected to one resonator grid of the tube and a center conductor connected to the other resonator grid of the tube, said outer conductor including two slab-like parallel conduct ing walls disposed upon opposite sides of the center conductor, end walls secured to the slablike walls and forming a mounting for the tube, and a rectangular plunger disposed between said walls and having a centra1 aperture to receive said center conductor, said plunger being adjustable toward or away from said end wall to adjust the frequency of operation, the cavity space between said slab-like walls being generally rectangular in cross section, and cavity mode suppressing means electrically connected to the resonator and disposed within that part of the cavity space which extends laterally between said slablike walls from one side of the center conductor. 6. A high frequency generator as in claim 5 in which said cavity mode suppressing means includes a probe, means carried by the plunger for mounting said probe, said mounting means permitting limited movement of the probe relative to the plunger in a direction corresponding to the direction of extent of the axis of the center conductor, and means serving to move said mode suppressing means relative to the plunger in response to movements of the plunger relative to said end wall.

WILLIAM R. HEWLETT.

HOWARD M. ZEIDLER.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 2,422,695 McRae June 24, 1947 2,436,397 Morton Feb. 24, 1948 2,450,026 Tomlin Sept. 28, 1948 2,504,329 Heising Apr. 18, 1950 

